The present invention relates to the field of data communications in general and more particularly, to ride matching systems.
Wireless communication systems (networks) are commonly employed to provide voice and data communications to subscribers. For example, analog cellular radiotelephone systems, such as those designated AMPS, ETACS, NMT-450, and NMT-900, have long been deployed successfully throughout the world. Digital cellular radiotelephone systems such as those conforming to the North American standard IS-54 and the European standard GSM have been in service since the early 1990's. More recently, a wide variety of wireless digital services broadly labeled as PCS (Personal Communications Services) have been introduced, including advanced digital cellular systems conforming to standards such as IS-136 and IS-95, lower-power systems such as DECT (Digital Enhanced Cordless Telephone) and data communications services such as CDPD (Cellular Digital Packet Data). These and other systems are described in The Mobile Communications Handbook, edited by Gibson and published by CRC Press (1996).
As the wireless communication industry continues to advance, other technologies are being integrated within these communication systems in order to provide value-added services. Recent governmental mandates, e.g., the response time requirements of the FCC Phase II E-911 service, make it imperative that the position of a mobile handset be determined accurately and in an expedited manner. One technology being considered to facilitate location determination is the global positioning system (GPS). Briefly, as illustrated in FIG. 1, GPS is a space-based triangulation system using satellites 52 and computers 58 to measure positions anywhere on the earth. GPS was first developed by the United States Department of Defense as a navigational system. The advantages of this navigational system over other land-based systems are that it is not limited in its coverage, it provides continuous 24-hour coverage, regardless of weather conditions, and is highly accurate. While the GPS technology that provides the greatest level of accuracy has been retained by the government for military use, a less accurate service has been made available for civilian use. In operation, a constellation of 24 satellites 52 orbiting the earth continually emit a GPS radio signal 54. A GPS receiver 56, e.g., a hand-held radio receiver with a GPS processor, receives the radio signals from the closest satellites and measures the time that the radio signal takes to travel from the GPS satellites to the GPS receiver antenna. By multiplying the travel time by the speed of light, the GPS receiver can calculate a range for each satellite in view. Ephemeris information provided in the satellite radio signal typically describes the satellite's orbit and velocity, thereby generally enabling the GPS processor to calculate the position of the GPS receiver 56 through a process of triangulation.
A variety of mobile terminal (MT) location techniques have been proposed. These location techniques include those based solely on the wireless network signals, Global Positioning System (GPS) based approaches and assisted GPS approaches combining communication signals and GPS signals.
Taylor et al., U.S. Pat. No. 4,445,118, discusses the concept of aiding or assisting GPS receivers. The assistance information allows the position computation function (PCF) to be done in the user receiver. Lau, U.S. Pat. No. 5,418,538, describes a system and method for aiding a remote GPS/GLONASS receiver by broadcasting “differential” information from a like receiver in a “reference station.” Eshenbach, U.S. Pat. No. 5,663,735, describes a method whereby a GPS receiver derives an accurate absolute time reference from a radio signal. The GPS receiver performs the position calculation, and therefore must have the absolute time as well as the ephemeris and clock corrections for the GPS satellites. Another assisted-GPS standard for GSM-based networks is described in specification numbers 3GPP TS 04.31 and 3GPP TS 03.71. This standard is based on placing reference GPS receivers at various nodes in the network, capturing the ephemeris information from these receivers, then providing this information along with a list of visible satellites to all handset-based GPS receivers via messages on GSM downlink bearers. The benefit of this approach is that it allows the handset-based GPS receiver to be fully functional, i.e., it contains the PCF and also can operate in continuous navigation mode.
Another approach to a reduced complexity GPS location service to satisfy governmental mandates for FCC Phase II E-911 service provides only a simplified, GPS receiver in the MT, rather than a fulll function autonomous GPS receiver. An assisted location service associated with the communication network then is used to calculate the position of the MT. Such an approach is specified in the TIA/EIA/IS-801-1 specification (IS-801), which is implemented in the GPSOne protocol assisted location service available from SnapTrack Inc, a Qualcomm Company, as described at the website http://www.snaptrack.com. A GPSOne compatible receiver (i.e. located in the mobile terminal) generally performs all GPS satellite acquisition functions and then sends measurements to a centralized location server of a CDMA network serving the mobile terminal. By generating only intermediate navigation data at the GPSOne compatible receiver, some of the burden of performing positioning calculations may be shifter to the location server.